1. Field of the Invention
The present invention relates to a control device in a car for controlling the equipment in the car in response to the road condition as well as a device for detecting the road condition in driving the car.
2. Description of the Prior Art
Road condition affects the driving perception of the operator of a car, easiness of driving (driving character), and safety of car operation.
Shock absorbers are provided on the car, and though the shock absorber decreases transmission to the car body of vibration of the car wheel, since the attenuating capacity of shock absorbers affects the pitching and rolling of the car or its driving character, there has been an art for automatically detecting the driving condition of the car and establishing the attenuating capacity accordingly by providing an attenuating capacity control mechanism for the shock absorber, responsive to the operation of a manual instruction switch or automatic control; and since it is desirable to perform lowering of the car body for the purpose of increasing the safety of the car in high speed driving, there has been an art for establishing the car level appropriately by providing a car level control device for the car, responsive to the operation of a manual instruction switch, or automatic control (for example: Japanese Patent Application Laid-Open Publication Sho-59-17599)
Further, when applying a sudden braking action in case of the road surface being dirtied by oil or being frozen, the car wheel stops rotating due to the braking force while the car wheel skids against the road, and control of the car in the forward direction using the steering wheel becomes difficult, and braking distance becomes extended In order to prevent this, it is desirable to assemble an anti-skid control device for automatically reducing the car wheel brake pressure by detecting a slipping rate of the car wheel to the car in case the possibility of skidding is high (for example: Japanese Patent Application Laid-Open Publication Sho-62-270795).
In the above-described attenuating capacity control of shock absorbers, car level control and anti-skid control according to road condition, it is desirable to change the control characteristic. For example, in the case when road vibration increases, it is preferable to make the attenuating capacity of the shock absorber greater and raise the car level. And, in a car equipped with an anti-skid control device, since a relation with respect to the frictional coefficient .mu. of car wheel against the road surface and the slipping rate of the car wheel is changed according to the road condition, for example, as shown in FIGS. 7d-7g, it is preferable to control the car wheel brake pressure so as to create the slipping rate bringing the maximum value of the frictional coefficient .mu..
In order to carry out the desired control in response to the road condition as above, it is required to detect the road condition.
In Japanese Patent Publication Sho-58-58254, a vibration detector is provided on a car, and when a peak vibration of the car body exceeds a predetermined value, during a predetermined period of time from that time, the sensitivity of anti-skid control is maintained at a lower level. And, in Japanese Patent Laid-Open Publication Sho-60-22548, there is proposed counting the number of times that the peak car wheel acceleration exceeds the predetermined value, and when the counted value exceeds the predetermined value, lowering the sensitivity of anti-skid control. Further, in Japanese Patent Laid-Open Publication Sho-60-107440 and Patent Laid-Open Publication Sho-60-255558, there is proposed detecting a vibrating frequency of car wheel speed or car wheel acceleration, and when it exceeds a predetermined frequency, lowering the sensitivity of anti-skid control.
In aforementioned conventional road condition detection, generally speaking, a binary value is detected by treating the road as either good or bad, and specifically, in said Japanese Patent Laid-Open Publication Sho-60-22548, when a vibration detector detects the vibration exceeding a predetermined level at any time, a detecting signal representing bad road is generated, and maintained during a predetermined period of time from that time. Therefore, detecting accuracy is extremely coarse, and the probability of error in detection is high. Since the sensitivity change of anti-skid control based on such detection delays the pressure reduction of car wheel brake pressure, the problem is that it becomes hard to obtain the effect of anti-skid control.
Since said Japanese Patent Laid-Open Publication Sho-60-22548 discloses when peaks over a predetermined level arise more than a predetermined number of times within a predetermined period of time, thus detecting a bad road, and since Japanese Patent Laid-Open Publication Sho-60-107440 and Japanese Patent Laid-Open Publication Sho-60-255558 disclose detecting the road condition on the basis of vibrating frequency, it is suspected that detecting accuracy of the road condition here is rather high, but the result of detection is a binary value of good/bad, and therefore, it is appreciated that there are problems in adjustment of anti-skid control corresponding to the road condition is coarse, and also the problem that it becomes hard to obtain the effect of anti-skid control.